TOPEKA, Kan. The Kansas Board of Education, long ridiculed for its resistance to teaching evolution, prepared today to repeal rules backed by social conservatives and switch to science guidelines that embrace Charles Darwin s mainstream theories.

The new board, with a 6-4 majority of Democrats and moderate Republicans, was to debate and vote on what would be the fifth set of science standards for public schools in eight years.

The existing standards suggest widely accepted evolutionary concepts like a common origin for all life on Earth and changes in one species leading to a new one are challenged by new evidence. Those rules, adopted in 2005, were pushed by supporters of intelligent design, which holds that life is so complex that it must have been created by a higher authority.

An alternative, drafted by scientists and educators, would treat evolution as well-supported by research. It also...